The present invention relates to optical scanning systems and more particularly to an optical bar code scanning system in which the bar code can be positioned at various distances from the scanner during a scanning operation.
In present-day merchandising point-of-sale operations, data pertaining to the purchase of a merchandise item is obtained by reading data encoded indicia such as a bar code printed on the merchandise item. In order to standardize the bar codes used in the various point-of-sale checkout systems, the grocery industry has adopted a uniform product code (UPC) which is in a form of a bar code. Various reading systems have been constructed to read the bar code, including hand-held wands which are moved across the bar code, stationary optical reading systems normally located within a check-up counter in which the bar code is read when a purchased merchandise item is moved across a window comprising the scanning area of the counter and portable stand-alone desk-top laser scanning work stations which include a laser scanning head mounted above a support base and facing the operator in which objects bearing bar code symbols which are to be scanned are passed underneath the head. In each of these prior scanning systems, the projected scanning light beams are all focused in a singe plane which is located in the plane of movement of the object bearing the coded label or in the case of hand-held scanning systems in a plane in which the bar code label is positioned. Since many merchandise items support the coded label at various angles to the focal plane of the scanning unit, complex and expensive optical systems have been developed to transmit the scanning light beams at different angles to cover all possible orientations of the bar code label to ensure a valid scan operation. This requirement limits the operating efficiency of the scanning systems, while increasing their cost. In the case of overhead bar code scanning systems, the positioning of the bar code label with respect to the scanning head is very critical to the reading of the bar code label. It has been found that the operator has trouble locating the bar code label in the focal plane of the scanning system which requires the scanning operation to be repeated thereby increasing the time of processing the merchandise item.